string-manipulation-mastery

## CRITICAL GUIDELINES

### Windows File Path Requirements

**MANDATORY: Always Use Backslashes on Windows for File Paths**

When using Edit or Write tools on Windows, you MUST use backslashes (`\`) in file paths, NOT forward slashes (`/`).

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# Bash String Manipulation Mastery (2025)

## Overview

Comprehensive guide to string manipulation in bash using parameter expansion, pattern matching, regular expressions, and built-in transformations. Master these techniques to avoid spawning external processes like `sed`, `awk`, or `cut` for simple operations.

## Parameter Expansion Basics

### String Length

```bash
#!/usr/bin/env bash
set -euo pipefail

str="Hello, World!"

# Get length
echo "${#str}"  # 13

# Length of array element
arr=("short" "much longer string")
echo "${#arr[0]}"  # 5
echo "${#arr[1]}"  # 18

# Number of array elements (not string length)
echo "${#arr[@]}"  # 2
```

### Substring Extraction

```bash
#!/usr/bin/env bash
set -euo pipefail

str="Hello, World!"

# ${var:offset} - from offset to end
echo "${str:7}"     # World!

# ${var:offset:length} - from offset, length chars
echo "${str:0:5}"   # Hello
echo "${str:7:5}"   # World

# Negative offset (from end) - note the space or parentheses
echo "${str: -6}"      # World!
echo "${str:(-6)}"     # World!
echo "${str: -6:5}"    # World

# Last N characters
last_n() {
    local str="$1" n="$2"
    echo "${str: -$n}"
}
last_n "Hello" 3  # llo

# Extract between positions
between() {
    local str="$1" start="$2" end="$3"
    echo "${str:start:$((end - start))}"
}
between "0123456789" 3 7  # 3456
```

### Default Values

```bash
#!/usr/bin/env bash
set -euo pipefail

# ${var:-default} - use default if unset or empty
name="${1:-Anonymous}"
echo "Hello, $name"

# ${var:=default} - assign default if unset or empty
: "${CONFIG_FILE:=/etc/app.conf}"

# ${var:+alternate} - use alternate if var IS set
debug_flag="${DEBUG:+--verbose}"

# ${var:?error} - exit with error if unset or empty
: "${REQUIRED_VAR:?REQ